1. Field of the Invention
This invention relates to motion activated lights.
2. Description of the Related Art
Decorative outdoor lanterns for residential and commercial lighting applications have been popular for many years. In the past six years or so, motion sensors have been added to such lanterns to provide more convenience, energy savings, and security for the user. Passive infrared (PIR) sensors have been developed and utilized in various such lanterns to sense the approach or motion of a person. The light fixtures turn on when someone moves into the sensor's field of view, and then automatically turn off when the motion ceases.
Infrared radiation is the physical means of detection of such fixtures, there being a known relationship between the wavelength of the strongest infrared radiation and the temperature of the body emitting it. Thus, the body of a human, as well as that of some other animals, radiates the strongest infrared radiation between 9 .mu.m and 10 .mu.m. Infrared radiation can be detected due to the "pyroelectric effect", which is due to the generation of a surface electric charge on certain dielectric crystalline materials when exposed to infrared radiation, which differs from the "natural charge" at thermal equilibrium that is present due to spontaneous polarization. The current which flows when there is a temperature change and resultant change in surface charge can be measured by means known in the art, for example, by connecting a high impedance resistor between the electrodes of both crystal surfaces and reading the voltage drop.
An improvement in infrared detection devices occurred when the optical system was developed to include a number of facets in an associated reflector and/or one or more lenses, which were oriented so that radiation originating in the particular ranges of angular scan of the lenses was sequentially directed to a group of thermal detectors (See for example, U.S. Pat. No. 3,958,118 of Schwartz).
Motion activated light fixtures now generally utilize infrared sensors, together with an optical collecting and focusing means such as a system of Fresnel lenses. The aggregate of the individual fields of view of the multiple Fresnel lenses defines the overall field of view of the device. Generally, the lens plates to which the Fresnel lenses are mounted are curved sections from a cylindrical surface, with the Fresnel lenses being mounted in parallel rows. Examples include various fixtures sold by Regent Lighting Corporation (e.g., Model Numbers MS35, MS30 and MS80). Fresnel lenses, each of which is made of a surface of a series of concentric circular prisms, collect radiation from a moving object and direct the energy to a detector. The detector can be a thermistor in which resistance changes with a change in the energy level, or more generally, a pyrosensor which generates a voltage or alters a current passing through it. Such fixtures also comprise one or more signal amplifiers and a control circuit.
Early lantern designs housed the motion detectors D in a large backplate that the decorative fixture was attached to, as shown in FIG. 1. Such motion detectors were visible and clearly affected the decorative appearance of the fixture. Also, they often meant that certain decorative features of the fixture had to be removed or altered, for example, the lower tail present on many fixtures would obscure the field of view of the sensor.
Other lanterns have been designed with the motion detector D located in a clearly visible window in the base of the fixture itself as shown in FIGS. 2 and 3. See also, U.S. Pat. No. 5,282,118 of Lee. In these cases, although the decorative appearance is less affected than by the earlier models, someone viewing the lantern can still tell that the lantern is a motion sensing lantern because the window that is necessary for the lens of the motion sensor is clearly distinguishable from the surrounding fixture material, even if the lens shape and color more closely blends with the lantern than in prior fixtures.
State-of-the-art motion detectors that claim to have "hidden" sensors generally utilize a modular construction because the small portion of the lamp where the sensor is located is not large enough to hold all of the electrical components. One part of the motion detector circuitry is connected to the remainder of the circuit by a connector cable threaded through the lantern fixture.
It is therefore an object of this invention to provide a motion activated decorative lantern which has a optical lens which becomes part of the lantern structure and appearance so that there is no profile difference due to the presence of the motion sensor, and which has no external cables other than power connections.
Prior motion detecting lanterns which may be adjusted so that the area viewed by the lantern changes have been made. Generally, this adjustment involved turning the base of the lantern so that the visible window rotates and is aimed in the area of detection. In these fixtures the direction of aiming is also visible to those the owner wishes to detect.
It is therefore a further object of the invention to provide a motion activated decorative lantern which allows adjustment in the detection area without the details of the adjustment being visible when the lantern is viewed.
Other objects and advantages will be more fully apparent from the following disclosure and appended claims.